Close to 42,000 customers are booked to fly with Air New Zealand that day.

Air New Zealand said last week the average income of the maintenance engineers, logistics and other staff to strike was $115,000 - and 170 of them earn more than $150,000.

AMEA lead advocate Stan Renwick told Morning Report that income included a "fair amount of overtime" and one of the union's biggest concerns was that people were fatigued.

Engineers were working in excess of 55 hours a week, he said, and overtime was generally for urgent jobs such as planes coming through that needed repairs.

"If you're a shift worker, and you're expected to work through the night and you're still expected to do your work at the end of the shift then there needs to be some penalties placed on the employer to prevent this happening.

"The argument basically is for penalty rates - that's a payment that's put against the employer to prevent excessive hours being worked. In this case it hasn't worked.

He said the union had been offered 2 percent for 12 months and another 3 percent for 18 months - contradicting Air New Zealand's statement that the second increase was also for 12 months.

"Overall, if you were to break it down, all that's basically been offered is two increases of two percent."

The union wants a three percent rise, he said.

"The only reason we're in a position we're in at the moment is because the employer has put up a number of clawbacks not only on the overtime but on things like sick leave and various other areas where we've traditionally enjoyed some benefits."

He said the strike would go ahead if the talks didn't reach a resolution.

"If we can't get it fixed this week then I guess the industrial action will take place."

Air New Zealand had declined a request for an interview on Morning Report. Last week it said striking staff were using peoples' hard-earned holidays as a bargaining chip.

It said staff had declined a proposal to standardise overtime pay to 150 percent of regular pay rate and a corresponding $6400 one off payment to address the change from the present mix of double time and time and a half.